1. Field of the Invention
The present invention relates to a collision detection system for detecting a collision of a vehicle to output a signal for actuating a device carried on the vehicle.
2. Description of the Prior Art
An air bag, which is expanded in a vehicular compartment to protect the passenger when the vehicle has its front or side hit by another vehicle, is inflated with the inert gas which is generated by an inflater forming part of an air bag type protecting system. Especially in an electric air bag system, a gas producing agent in the inflater is ignited in response to a signal which is outputted when a collision is detected by a collision sensor arranged in a predetermined portion of the vehicle body. Then, the air bag is instantly expanded by a large quantity of gas generated abruptly as a result of the ignition to extend into a space between the driver and the steering wheel, between the assistance driver and the dashboard, or between a passenger in another seat and the compartment's side wall such as the inner face of the side door thereby to protect the passenger against the so-called "secondary collision".
In case of this side collision, therefore, the amount of impact absorption is less due to the structural restriction of the vehicle body than in case of the front collision so that the expansion of the air bag has to be completed for a seriously short time. This makes it necessary to mount a collision sensor of high sensitivity in such a portion of the body as can detect the collision most quickly.
For example, FIG. 14 shows a system exemplifying the air bag system of the prior art for protection against a side collision, as disclosed in U.S. Pat. No. 4,966,388. In this system, a collision sensor 1 is attached to either the inside of the outer panel 3 of a side door 2 of a vehicle or a flat plate 4 arranged in the side door 2. This collision sensor 1 is of contact type or pressure sensitive type for detecting a side collision when compressed at the time of a collision together with the member carrying it. If the side collision is detected, the sensor 1 outputs an ignition signal to ignite an inflater 5 so that an air bag 6 is inflated with the much gas generated by the inflater 5, to extend in the space between a passenger 7 and the inner face of the side door 2. Thus, the passenger 7 can have his head 8 or the like protected against the secondary collision against the side wall of the compartment.
As described above, the side collision sensor 1 of the prior art is attached to such a portion in the side door 2 as can detect the side collision most easily. The side collision sensor 1 is crushed, for example, by a load, which is caused by the deformation of the side door 2 due to the side collision, to have its paired contacts connected to output the ignition signal for expanding the air bag.
Here, the patterns to be conceived as the side collision of the vehicle are classified into: side collisions generally at a right angle, as shown in FIG. 16; oblique collisions at an angle, as shown in FIG. 15; and local collisions against obstacles such as telegraph poles. The manners for the load to be applied from the collisions are different in the patterns. In case the side door is hit generally at a right angle by the head of another vehicle, for example, the area to receive the load is widened to decrease the collision load per unit area. In case, on the other hand, the side door is hit by a slender obstacle such as a telegraph pole, the load per unit area is high although the area to receive the load is small and the total load is low. These various kinds of collisions have to be detected without fall by the aforementioned collision sensor 1 of the air bag system for protection against a side collision. It is, therefore, the current practice that the collision sensor 1 of high sensitivity is attached to such a portion, e.g., inside of the outer panel 3 of the side door 2 or on the flat plate 4 in the door as can detect the side collision relatively easily.